Polymers and copolymers that contain amino groups are useful for many applications, depending on the concentration of amino groups present. When the amino content is low, these groups function as sites for crosslinking or curing, as sites for binding dyes or stabilizers and as reactive sites for other chemical and biochemical purposes. When the amine content is high, the polymers can function as ion-exchange resins if crosslinked or as a water soluble polyelectrolyte if not crosslinked.
Polymers that contain amino groups are prepared by three methods: (a) by direct polymerization of an unsaturated amine such as p-aminostyrene; (b) by polymerization of unsaturated amides, imides or urethanes, followed by hydrolysis of the amide, imide or urethane groups on the resulting polymer to thereby generate amine groups on the polymer; (c) by chemical modification of polymers, as for example, by reducing nitrated polystyrene to obtain polyaminostyrene or by reducing polyacrylamide to obtain polyalkylamine. These methods can also be used to prepare copolymers of amine-bearing monomers with other monomers.
When polymers and copolymers of vinyl amine are prepared, only method (b) mentioned above is appropriate because vinyl amine is unstable. Indeed, poly(vinylamine) has been prepared by hydrolysis or aminolysis of poly(N-vinyl phthalimide), poly(N-vinyl acetamide) and poly(t-butyl N-vinyl carbamate). Copolymers of N-vinyl phthalimide, N-vinyl acetamide, t-butyl N-vinyl carbamate or related monomers with other vinyl monomers, such as ethylene and vinyl chloride can be prepared by conventional free radical polymerization techniques that are well known in the art, but it is difficult to prepare copolymers of the vinyl amine derivatives with highly reactive vinyl monomers such as styrene, acrylate esters, methacrylate esters and acrylonitrile. It is especially difficult to prepare such copolymers if the content of vinyl amine derivative is high, greater than 40 percent, for example. Although previously available techniques may have been limited in the amount of vinyl amine derivative monomers that could be incorporated into copolymers, the amide, imide or carbamate protecting groups of the vinyl amine derivatives could be removed by hydrolysis, hydrazinolysis or aminolysis reactions.
It is known that copolymers having an alternating arrangement of monomer units can be prepared by copolymerizing vinyl monomers containing electron releasing substituents (methyl, phenyl, ether) with vinyl monomers containing electron attracting substituents (nitrile, ester, ketone) in the presence of Lewis acids such as ZnCl.sub.2, BCl.sub.3, EtAlCl.sub.2, ethyl aluminum sesquichloride, etc. Information on this topic is discussed in reviews of Hirai [J. Polymer Science, Macromolecular Reviews, 11, 47 (1976)], and Furukawa [Rubber Chem. and Technol., 53, 600 (1978)], and Hirooka [Pure and Applied Chemistry, 53, 681 (1981)].
However, no one has previously prepared alternating copolymers of amino group bearing monomers or their derivatives with other monomers. We have discovered that with certain derivatives of amino group bearing monomers, it is possible to prepare alternating copolymers such as N-vinylphthalimide or N-(4-vinylphenyl)phthalimide with methyl acrylate or other monomers that contain electron accepting groups, if the copolymerizations are conducted in the presence of Lewis acids, such as ethyl aluminum sesquichloride. The resulting copolymers can be converted into copolymers containing amino groups by reaction with hydrazine. When the copolymers also contain ester groups, as in the case of copolymers containing methyl acrylate units, hydrolysis of the ester groups as well as generation of the amino groups can yield a copolymer containing an alternating sequence of amino and carboxylic acid groups. Polymers of this type have not been known previously.